Process of cracking hydrocarbons



Jan. 26, 1932. E. c. HERTHEL.

PROCESS OF CRACKING HYDRQCARBQNS Filed Aug. 18, 1926 INVENTOR fo ene 6.6 67%?! 0 BY flak A ATTORNEYS Patented Jan. 26, 1932 rrEo STATES PATENT?OFFICE EUGENE.G. HERTI'IEL, OF CHICAGO, ILLINOIS, ASSIGNOR TO SINCLAIRREFINING COMPANY, OF NEWYORK, N. Y., A CORPORATION OF MAINE l thesesurfaces.

PROCESS OF CRACKING I-IYDROOARBONS Application filed August 18, 1926.Serial No. 130,050.

My invention relates to improvements in the cracking of higher boilinghydrocarbon oils to form lower boiling hydrocarbon oils therefrom bydistillation at a cracking temperature under pressure. This applicationis in part a continuation of my prior application filed July 12, 1922,Serial No. 574,380, and my present invention relates particularly toimprovements in the treatment of relatively light hydrocarbon oils, suchas kerosene, for the production of gasoline or pressure distillate ormotor spirit according to the general process there described.

In carrying out the process of my said prior application, a liquid bodyof the hydrocarbon oil to be cracked is subjected to distillation at acracking temperature and under superatmospheric pressure, vapors beingtaken off under superatmospheric pressure, and fresh oil is supplied toand tarladen oil withdrawn from the liquid body as the operationproceeds, the supply of fresh oil to and withdrawal of tar-laden oilfrom the liquid body being regulated to prevent saturation of the oil inthe liquid body and pitch or pitchy constituents and so that such pitchand pitchy constituents are held in solution in the oil body and in thetar-laden oil as withdrawn. As further described in my said priorapplication, the. supply of fresh oil and withdrawal of tar-laden .011are regulated so that at no time more than 50% of the total stock,including feed oil, has been taken off as distillate. The formation ofcarbonaceous deposits upon the heating surfaces of the still by cokingthereon of pitch or pitchy constituents precipitated from the oil isthus prevented; several im portant advantages being thereby secured,among which may be mentioned prolongation of the period of operation andthe avoidance or retardation of the formation of carbonaceous depositsupon the heating surfaces of the still actin as an insulating layer uponIn carrying out my present invention, likewise, the operation isconducted so that the body of oil undergoing distillation does notbecome saturated with pitch or pitchy constituents duringthe operationor at least not until just prior to'the time when it is desired toterminate the operation.

My present invention relates particularly tothe treatment of hydrocarbonoils of which more than about boils off at 500 F. and of which not lessthan about 80% boils off at 600 F. upon fractional distillation underatmospheric pressure. The following distil lation figures were takenfrom an oil typical of those to the treatment of which my presentinvention relates. This oil had a gravity of 309 Be, an initial boilingpoint-of 426 F., and 55.7% came off up to 500 F.

10% oft at 403 F. Gravity of fraction 40.6 Be. 200/, off at 471 F.Gravity of fraction 39.9 Be. off at 478 F. Gravity of fraction 39.4 Be.400 off at 486 F. Gravity of fraction 88.9 Be. off at 495 F. Gravity offraction 38.G Be. 6007,, off at 507 F. Gravity of fraction 38.0 Be. offat 524 F. Gravity of fractioi1 372 Be. 800/, off at 548 F. Gravity offraction 36.6" 900A off at 586 F. Gravity o1 fraction 35.9 Be. Bottoms315 B.

According to my present invention, a

charge of such relatively light oils is distilled at a crackingtemperature under a pressure upwards from 125 pounds per square inch,and fresh oil is supplied to and tar-laden oil withdrawn from the chargeof oil undergoing pressure distillation during the operation, the supplyof fresh oil and the withdrawal of tar-laden oil being regulated so thatthe amount of oil taken off as distillatedoes not substantially exceedabout 60% of the total oil, including the original charge of oil and thefresh oil supplied during the operation. Petroleum oils of the characterspecified are relatively refractory and do not break down as readily asoils of lower boiling range. The tendency to formation of very heavypitches or heavy coking of solid or semi-solid matter is materiallyreduced and the pitches formed are less dense. As a consequence, theconcentration of pitch in the body of oil undergoing pressuredistillation can be carried to a higher degree before the saturationpoint is reached. Thus, although the percentage of the oil taken off asdistillate may be increased in carrying out the present invention,ohjectionable deposition of carbonaceous material within the pressurestill is nevertheless avoided. Oils of the character specifiedalsovaporize very readily and have a tendency to escape as a vaporbefore being broken down to a suliicient extent. In carrying out myinvention, this tendency is counteracted by employing pressures of 125pounds per square inch or more. With such relatively high pressures,vaporization is retarded making more heat available for cracking and thetemperature of the body of oil undergoing distillation is also increasedassisting in increasing the rate at which cracking proceeds.

Likewise, in carrying out my invention, it is advantageous to subjectthe vapors from the pressure still to a refluxing, operationby directcontact and heat exchange with fresh oil supplied to the operation at,a. rate sub.- stantially in excess of the rate at which oilis taken oflias distillate. Fresh oil lot the character to the treatment 1 of whichthe invention particularly relates may, for example, be so supplied at arate corresponding to from 170% to 200% or more of the rate at whichdistillate isv removed. Preheating the fresh. oil in this manner alsotends to increase the temperature of the body ofoil undergoingdistillation, thus assisting inincreasing the. rate at which crackingproceeds. When higher pressures. are. employed, the rate at which freshoil is. so supplied may be decreased, and any additional fresh-oilftobe.

,densed pressuredi-stillate or a fraction of corresponding charactersuch that. it would substantially completely vaporized the tower withthe consequent cooling and-refluxing action-without however, increasingthe volume of oil inthe. pressure still.. Adequate refluxing action maythus be secured without limiting the percentageof. the oil which may betaken oil as distillate up; to the limits where objectionable depositionof can aceous material isinvolved. Oil can-- ployed as such asupplemental refluxing medium may be introduced either in admixture.with the. fresh oil supplied to the cracking operation or it may beseparately introduced intothe refluxing operation.

One form of apparatus adapted for carry ing out .the presentinvention-is diagrammati cally illustrated in the accompanying drawing,and the inventionwill be further described in connection therewith. Thepres sure still illustratedlis of the general construction describedandillustrated in Letters Patent: No. 1,285,200 issued to the Sinclair.Refinin Company, November 19, 19-18, on anappfication. of Edward W.Is'om, but it;

will be appreciated that my invention is useful in connection with othertypes of pressure cracking stills.

Referring to the drawings, the pressure still proper comprises a bulksupply tank 1 adapted to contain a body of oil and located away from abattery of heating tubes 2 with circulating connections 3, 4 and 5including a circulating pump 6 for circulating oil from the bulk supplytank upwardly through the heatingtubes and'back to the bulk supply tank.A connection is provided at 7 for with drawing tar-laden oil from thebody of oil in the bulk supply tank 1, and a connection is shown at 8for supplying fresh oil directly to; the. stream of oil circulatingthroughthe pump-6 to the heatingtubes. A refluxtower 9 isarranged abovethe bulk. supply tank and. is connected thereto by a vapor. line 10through which vapors escaping from the bulk supply tank enter the lowerend of the. refluxtower. The Y vapors; escaping micondensed from the.reflux tower. pass to a, suitable condenser (not. shown) throughconnection 11 where they are. condensed to form the pressure distillate.The pressurewithin the system: may be maintained by valves (not shown)located-in the vapor line between the reflux tower andthe condenser orby. valves arranged beyond the condenser, A connection 12 is providedfor introducing'freshoil directly into. the upper end of the refluxtower. Any, oil employed as a. supplemental refluxing agent may beintroduced into the refluxto-wer through this connection in ad mixturewith fresh oil, ore separate. connection. may bet-provided for.introducingv such oihndvantageously' at a point in the reflux towerabovethe: at: which the fresh oil is introduced. Reflux'and admixed fresh oilcollecting in; the lower end of the. reflux tower are supplied to thecirculating stream of oil entering the circulating pump 6 through connection 1.3...

In carrying out the inventionin apparatus. of the type-(illustrated, thepressure stillis'. charged withsay 8,000 gallons of a. stock ofwhich-more.- than about 2.5% boils. oil at 506 F.. and brought to acracking temperature; under a pressure upwards of 125 pounds per:squareinch; The. introduction of fresh oil into tl'xeup-per end ofthetoweris then begun and vapors. are taken ofii and condensed-to form thepressure distillate. Distillates may be taken ofii, for example, at'arate. of about 750 gallons: per and fresh oil supplied ata rate-of about1,000 gallons per hour or somewhat more. Before the concentration ofpitch in: the. still charge:- reachessthe. saturation pointnthe-Withdrawal of tar: is: begun Initially, the. tar maybe withdrawn at arate; of from 800 to 1,000.-

per hour, until the still charge is reduced approximately to the amount;of the charge before the introduction. of fresh oil isbcgan and the ratethensomewhat reduced but maintained sufficient to prevent theconcentration of pitch exceeding the saturation point. Any additionalfresh oil required to maintain the charge in the still is introducedthrough the circulating pump. The amount of additional fresh oil sointroduced through the circulating pump may vary over wide limits. Inpractice the apparatus illustrated and described in this application hasbeen found to operate satisfactorily when additional fresh oil is introduced through the circulating pump at a rate of about 250 gallons perhour or some what more. Any additional refluxing required may be securedby returning and reintroducing into the reflux tower a part of thepressure distillate. An amount of pressure distillate corresponding toas much as 25% or somewhat more of the fresh oil introduced into thereflux tower may, for example, be so returned. The distillation isterminated before the percentage of the oil taken off as distillatesubstantially exceeds 60% of the total oil supplied to the operation,including the original charge and the fresh oil supplied during theoperation. The actual length of time during which the operation iscontinued will vary over wide limits depending on the rate at whichfresh oil including any additional fresh oil supplied through thecirculating pump is introduced to the system. In the foregoing example,however, in which fresh oil including that introduced through thecirculating pump, is introduced to the system at a rate of about 1250gallons per hour and distillate is taken off at a rate of about 750gallons per hour, the distillation may be terminated with advantageafter distillate has been taken off for a period of approximately 200hours at which time the total distillate taken off would amount to 58%of the total oil supplied to the system including the initial charge. Ifthe major portion of the distillation has been carried out in accordancewith my invention, the withdrawal of tar-laden oil may be stopped ordiminished and the operation of the pressure still continued for afurther brief interval to obtain an additional amount of distillate.This, however, entails danger of deposition of carbonaceous materialwithin the still, although only at the end of the operation and justbefore it is terminated.

I claim:

1. A process of cracking higher boiling hydrocarbons to form lowerboiling hydrocarbons, which comprises heating a liquid body ofhydrocarbon oil of which more than about 25% boils off at 500 F. and notless than about 90% at 600 F. at atmospheric pressure to a crackingtemperature under superatmospheric pressure upwards of 125 pounds persquare inch by circulating oil from said liquid body through heatingtubes and back to said body, taking ofi vapors from said liquid bodyunder pressure while continuing the heating operation, supplying freshhydrocarbon oil of the same character to and withdrawing tar laden oilfrom the said liquid body of oil as the operation progresses, andregulating the supply of fresh oil and the withdrawal of tar laden oilso that throughout the major portion of the operation the amount of oiltaken off as final distillate exceeds 50% and does not substantiallyexceed about 60% of the total oil supplied to the operation includingthe original liquid body of oil and the fresh oil supplied during theoperation.

2. A process of cracking higher boiling hydrocarbons to form lowerboiling hydrocarbons, which comprises heating a liquid body ofhydrocarbon oil of which more than about 25% boils off at 500 F. and notless than about 90% at 600 F. at atmospheric pressure to a crackingtemperature under superatmospheric pressure upwards of 125 pounds persquare inch by circulating oil from said liquid body through heatingtubes and back to said body, taking off vapors from said liquid bodyunder pressure while continuing the heating operation, subjecting thevapors to a refluxing operation in which fresh hydrocarbon oil of thesame character is introduced into direct contact with the Vapors andfrom which the admixed, refluxed and unvaporized fresh oil is returnedto the said liquid body, withdrawing tar laden oil from the said liquidbody as the operation progresses, and regulating the supply of fresh oiland the withdrawal of tar laden oil so that throughout the major portionof the operation the amount of oil taken off as final distillate exceeds50% and does not substantially exceed about 60% of the total oilsupplied to the operation including the original liquid body of oil andthe fresh oil supplied during the operation.

3. A process of cracking higher boiling hydrocarbons to form lowerboiling hydrocarbons, which comprises heating a liquid body ofhydrocarbon oil of which more than about 25% boils ofif at 500 F. andnot less than about 90% at 600 F. at atmospheric pressure to a crackingtemperature under superatmospheric pressure upwards of 125 pounds persquare inch by circulating oil from said liquid body through heatingtubes and back to said body, taking off vapors from said liquid bodyunder pressure while continuing the heating operation, subjecting thevapors to a refluxing operation, introducing into direct contact withthe vapors in the refluxing operation fresh oil of the same characterand an oil of the character corresponding to that of the distillatetaken off, returning the admixed, refluxed and unvaporized components ofthe oil introduced into the refluxing operation to the said liquid body,withdrawing tar laden oil from the said liquid body and regulating thesupply of fresh oil and the withdrawal of tar laden oil so thatthroughout the major portion of the operation the amount of oil takenoff as final distillate exceeds 50% and does not substantially exceedabout 60% of the total oil supplied to the operation including theoriginal liquid body of oil and the fresh oil supplied during theoperation.

In testimony whereof I affix my signature.

EUGENE C. HERTHEL.

